Conventionally, for the safety of automobiles, automotive body structures or the like have been developed in terms of how to save a pedestrian and protect an occupant when the pedestrian and an automobile crash into each other. However, in recent years, with the advancement of an information processing technology and an image processing technology, a technology to detect a person and an automobile at a high speed is being developed. By applying these technologies, an automobile that prevents an occurrence of a crash by automatically putting a brake before the automobile hits an object has already been developed. In automatic vehicle control, it is necessary to accurately measure a distance to an object, such as a person or some other vehicle; therefore, distance measurement using a millimeter wave radar or a laser radar, distance measurement using a stereo camera, and the like have been put to practical use. To put the above-described automatic vehicle control to practical use, it is necessary to detect objects that appear on a screen and perform control for each of the objects based on information obtained through the distance measurement using the above-described device. For example, it may be possible to change control depending on whether a detected object is a pedestrian or a vehicle.
If a distance is measured by using a stereo camera, it is possible to generate a disparity image based on an amount of deviation (disparity) between local areas captured by left and right cameras, and measure a distance between a subject vehicle and an object ahead of the subject vehicle. Then, through a clustering process of detecting a group of disparity pixels located at similar distances (with similar disparity values) as a single object, it becomes possible to detect the shape of a road surface on which the subject vehicle is running and an object (a person, a vehicle, a structural object, or the like) to be a target for crash avoidance or the like.
As an object recognition apparatus that estimates the shape of a road surface by using a disparity image, there is a disclosed structure that, to eliminate an influence of pitching, rolling, or the like of a subject vehicle, includes: a measuring means that divides an image obtained from a stereo camera into windows and measures a distance to an object for each of the windows; an estimating means that estimates an inclination of a road surface relative to the vehicle based on a distance of the road surface imaged by the stereo camera; a determining means that determines whether an imaging object is an obstacle or a character or a mark on the road surface for each of the windows based on the estimated inclination of the road surface; and a recognizing means that recognizes the object based on a determination result obtained by the determining means. In the structure, a distance from the subject vehicle to the road surface (a flat road surface) is calculated in advance and a distance is calculated for each of the windows based on the assumption that the road surface is flat (Japanese Patent Application Laid-open No. 2001-091217).